libnetconf2: Update to 0.12-r2

Cleaned up Makefile slightly. The removed CMAKE_OPTIONS are defaults from
cmake.mk

Removed Upstreamed patches.

Rebased and added .patch to the remaining one.

Added -Wformat-security patch.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/libnetconf2/patches/010-fix-format.patch

@@ -0,0 +1,11 @@
+--- a/src/io.c
++++ b/src/io.c
+@@ -62,7 +62,7 @@ nc_ssl_error_get_reasons(void)
+             ERRMEM;
+             return NULL;
+         }
+-        reason_len += sprintf(reasons + reason_len, ERR_reason_error_string(e));
++        reason_len += sprintf(reasons + reason_len, "%s", ERR_reason_error_string(e));
+     }
+ 
+     return reasons;